The following is information on ethylene damage to poinsettia plants.
Ethylene (C2H4) is an odorless, colorless gas which acts as a plant hormone, a growth regulator, and a potentially harmful pollutant of ornamental crops. Poinsettias demonstrate an interesting wilt like appearance (epinasty) after exposure to ethylene gas. Leaf epinasty has been observed when poinsettias were exposed to 10 ppm ethylene. Epinasty can be observed on poinsettia plants when they are kept in their shipping sleeves for a prolonged time. Petioles of poinsettias naturally produce ethylene in response to sleeving. Deformed top growth can also occur during long term exposure to ethylene. Preventing economic losses due to ethylene can be achieved by avoiding exposure to engine exhaust from shipping trucks and other combustion engine vehicles, ripening fruit, senescing plant materials, smoke, welding fumes, and poorly maintained greenhouse furnaces. Annually servicing boilers and burners may reduce or prevent ethylene damage to floricultural crops. Gas leaks resulting from cracked heat exchangers may allow harmful concentrations of ethylene to be released into the greenhouse. Continual expansion and contraction of the metal in the heat exchanger of a furnace can stress the welds resulting in cracks. Leaks at joints and seams can be discovered by painting soapy water on them. Another method of detecting leaks is the placement of smoke bombs or furnace candles within the firebox. Light or smoke penetrating from the interior should cause alarm to growers.
Information from the Poinsettia Problem Diagnostic Key on Physiological Disorders from North Carolina State University http://www.ces.ncsu.edu/depts/hort/poinsettia/corrective/a11.html